Fire: Friend and Foe

Posted by Marcia Penner Freedman

That fire requires oxygen is something children learn early in life. In a second grade science lesson a jar is placed over a flaming candle. The flame dies out. The wick smolders and cools.

Oxygen, heat and fuel, the fire triangle of the child’s lesson, has been fire’s story since its appearance on Earth, which, according to fire historian Stephen J. Pyne, was 400 million year ago, when all the ingredients were in place and the triangle was completed.

For 400 million years, fire has followed a consistent principle: after ignition – which occurs naturally in the form of lightning – sufficient heat, fuel and oxygen must be present if fire is to take hold and thrive. The removal or reduction of any one of these elements during a fire diminishes or extinguishes the fire’s energy.

How was it that human beings were able to grasp this principle and make fire their own? Perhaps they observed the slowing down of a forest fire when the nights turned cool, the halted progress as a fire crept up against a granite wall, or the flare up of flames in the presence of a sudden breeze.

Whatever it was that allowed them to connect the fire triangle dots, somewhere in the course of their evolution people learned they could start and stop fires and keep them going. They learned about fuels, figured out which burned hotter, which cooler. They put their fire triangle knowledge to use and manipulated fires of different types—to cook their food, clear their fields, shape their tools and weapons, run their cars, and, to fight their wildfires.

Anthropologist M. Kat Anderson, proposes that control of fire was “the greatest invention in the history of humankind,” allowing ancient people to stay warm, cook food and repel predators. Fire might have encouraged them to remain awake after nightfall, contributing to a social life, or prompted them to venture out and settle in otherwise forbiddingly cold areas.

Fire’s connection to humans is only one part of its narrative, however. As a force of nature, fire tears through the living world, feeding on biomass, drawing out its energy; in essence, killing it. “Hurricanes, tornadoes, floods, melting glaciers, these are purely physical,” wrote Pyne. “Not fires. Fires need life.”

Yes, fire feeds off of living matter. But in forests where fire is a natural part of the environment, like those in California, fire meets its match. It comes up against life that can resist its onslaught. It encounters plants that even depend on fire to sustain and improve their species.

In the Sierra National Forest, many examples exist of plants that have adapted to the presence of fire or make use of fire for propagation and improvement.

The ponderosa pine grows a bark thick enough to protect the tree from fire’s destructive heat. The dormant seeds of the Buckbrush burst open and germinate with fire, even when the mother plant has been killed. Flowering after fire is enhanced in the Mariposa Lily and Penstemon. In the ubiquitous Bear Clover, a.k.a. Mountain Misery, the deep and complicated root system and tenacious underground series of horizontal stems produce sprouts after the plant’s bout with fire.

Then there is the giant sequoia. In its relationship to fire, the sequoia resists fire by its rutted fibrous bark which has been known to grow to a thickness of two to three feet. The Sequoia defies fire by sending up shoots after fire has passed, the only conifer in the Sierra that sprouts.

The Sequoia also recruits fire to open its cones, which are the size of a chicken egg – two-and-a-half inches in length. A mature tree could have eleven thousand cones, but some can produce up to a hundred thousand. The cones, each containing an average of two hundred flakes of seed, can remain on the tree for decades waiting for heat from a fire to dry them and open them, releasing hundreds of thousands of seeds in the course of a year.

As they float to the ground, the seeds can travel up to six hundred feet from the base of the tree. Once the seeds settle, they need a soft rich soil in which to embed, a condition brought about by fire that cleans out the pine needles and other debris—duff—around the base of the tree. The seeds will become covered with a tiny layer of the mineral soil, and there germination begins.

What takes life, gives life.